Lead has been used for centuries in coatings, for example, as a pigment in paints, a corrosion inhibitor, and a drier in paints and varnishes. The primary reasons for using lead in coatings are properties such as durability of a finished coating, the broad spectrum of available colors using lead compounds, and corrosion, water, and weather resistance.
When lead-containing coatings age, the coatings deteriorate and consequently create lead-containing or lead-contaminated dust. Similarly, when lead-containing coatings are disturbed by cutting, drilling, sanding, or other methods commonly employed to remove building materials, lead-containing dust is released from the disturbed coating, and the dust can readily disseminate and contaminate large areas. This is a well-known public health hazard because lead-contaminated dust has been identified as a significant health hazard, particularly to children. Lead-based paints therefore were banned in 1978, but it is estimated that greater than 20 million homes may still contain lead-based coatings.
Lead contamination is not limited to paint and related products because lead has been used for decades in a wide variety of applications, such as building construction materials (roofing material, cladding, flashing, gutters and gutter joints, and on roof parapets), ammunitions, lead-acid car batteries, weights, fusible alloys, radiation shields (lead glass), and cosmetics. The use of lead in paint (wall paint, oil and water-based paint in art, paint used in toys), fuel, pipe, and plumbing material, solder for cars and pesticides has been greatly reduced over the last several decades because of the danger of lead poisoning.
Lead poisoning is a medical condition caused by increased levels of lead in the body. Exposure and accumulation to lead and lead-containing chemicals can occur through inhalation, ingestion, and/or dermal contact. Lead affects several organs in the body, and especially the nervous system. Lead also adversely effects bones (weakness in fingers, wrists, or ankles), teeth, kidneys (nephropathy and colic-like abdominal pain), the cardiovascular (blood pressure), immune, and reproductive (reduced fertility in males) systems, and can cause miscarriage in pregnant females. The adverse effects of lead on the nervous system is more pronounced in children than in adults.
Lead poisoning can be prevented by detecting lead or lead-containing compounds, and reducing or avoiding exposure to lead. To address the issue of the health risks from lead-containing dust, the United States Environmental Protection Agency (USEPA) promulgated regulations governing the appropriate methods and procedures to be used during remodeling and renovation of residential housing. These regulations stipulate that, for all housing built before 1978, the surfaces to be disturbed during renovation or remodeling must be checked for the presence of lead in the surface coatings. There are several ways lead testing can be accomplished, including Atomic Absorption spectroscopy, X-Ray Fluorescence, and chemical tests.
Atomic Absorption Spectroscopy and X-Ray Fluorescence involve sophisticated instrumentation and are expensive procedures. Several commercially-available, do-it-yourself lead test kits are available, but these kits are not quantitative and often lack credibility because they lead to false positive results. The chemical tests also often lack selectivity because test samples often contain additional compounds that can interfere with the assay for lead. Such additional compounds can include chromium, mercury, cadmium, zinc, barium, nickel, cobalt, copper, antimony, bismuth, titanium, and other metals present in pigments.
In addition, in order to achieve the different benefits of lead in various types of coatings, different forms of lead and lead-containing compounds have been incorporated into the coatings. Lead compounds that have been used in coatings include, but are not limited to lead sulfate, lead chromate, lead monoxide (litharge), lead silicate, lead sulfate blue basic, lead linoleate, lead naphthenate, and lead carbonate. While each type of lead compound has certain properties that differentiate the compound from the other lead compounds, the commonality of lead in each compound renders each compound a health risk. It is important that a detection method has the capability of detecting each type of lead compound that may be present in the solid sample. For example, some chemical assays fail to detect lead chromate.
In addition, although chemical tests to detect lead are commercially available, the tests may not properly detect lead levels at thresholds promulgated by regulatory authorities, e.g., lead equal to or exceeding 1.0 milligram per square centimeter (mg/cm2) or 0.5 percent by weight (equivalent to 5,000 parts per million or ppm). In such cases, either false positive or false negative results may arise, which in the case of a false negative can lead to health issues and in the case of a false positive to unneeded and expensive remediation measures.
A need therefore still exists in the art for a fast and accurate method and test kit to detect levels of lead in a solid sample, while avoiding false positive and false negative assay results. A method and test kit that can be used by a homeowner or in the field, without the need to submit samples for testing or to require substantial user training, also is an unmet need in the art.